The Freedom From Religion Foundation is countering the "Keep Christ in Christmas" billboards with its own "Keep Saturn in Saturnalia" ad – a reference to an ancient Roman god festival – which went up on Thursday in Pitman, N.J.

The atheist association, one of the largest in America, explained in a press release that the billboards are in a direct response to "Keep Christ in Christmas" displays by Roman Catholic society the Knights of Columbus. FFRF says that its local members were "stonewalled" in December 2012 when Pitman officials denied them a permit to display their "Saturn" banner, but allowed the Christmas one.

"FFRF first became involved in December 2011, when a resident reported the Christian banner as a potential state/church violation. Legal staff made numerous calls and sent messages to various public agencies and the Chamber of Commerce, including open records requests, and asked to erect FFRF's own banner, which wasn't allowed," the organization explained.

Saturnalia refers to an ancient Roman holy day celebrated on Dec. 17, on which religious rites were performed in honor of the god Saturn, also identified with the Greek god Cronus.

The atheist organization has been actively putting up displays this holiday season, and earlier this month posted a "Winter Solstice" sign at the Illinois Capitol in Springfield, claiming that there are no gods, angels, heaven or hell, and that religion "hardens hearts and enslaves minds."

"We don't think that religion, or irreligion, belong at the seat of state government. But if religious displays are going up in state capitols, then our display representing the freethought point of view will be there, too. In celebrating the Winter Solstice, we celebrate reality," said FFRF Co-President Annie Laurie Gaylor.

Dan Barker, FFRF co-president, added that Christians tend to think "they own the month of December. We don't agree. No month is free from pagan reverie!"

The Knights of Columbus have defended their "Keep Christ in Christmas" ads, however, and even started poster competitions where young people are encouraged to come up with a design that reflects the "true, spiritual meaning of Christmas."

The Catholic society explained that its initiative is supposed to combat the secularization of Christmas, by keeping the story of Christ in its center.

"The goal of this program is to create/increase awareness among young people about the true meaning of Christmas encouraging them to speak to other youngsters 'in their own language' to address the issues."